Cascaded H-bridge (CHB) based electric vehicle chargers are widely recognized for their modularity, scalability, and robust fault-tolerant capability. Such converters are often modulated using level-shifted carrier-based PWM (LSPWM) schemes due to computational simplicity and ease of implementation, but results in significant power imbalance among the modules. This power imbalance can be mitigated by reassigning carriers to modules, called Carrier-Reassignment PWM (CR-PWM). A First-In-First-Out (FIFO) based CRPWM is very easy to implement and provides some improvement over LSPWM, but fails to achieve perfect power balance. This paper proposes a novel carrier-reassignment scheme specifically designed for a 17-level CHB stage with eight reassignments per fundamental cycle, resulting in near-perfect power balance among modules. The redistribution of power also results in improvements in semiconductor losses - both conduction and switching loss. Loss models for the semiconductor devices were created through hardware double-pulse tests, SPICE and PLECS models, and integrated with MATLAB/Simulink to validate the proposed PWM scheme.

In this paper, we compare the performance of grid-forming (GFM) and grid-following (GFL) inverters during unbalanced grid faults. By performing an exhaustive time-domain electromagnetic transient (EMT) simulation study of an allinverter network, we compute a variety of transient and steadystate fault signatures including peak current, transient time, sequence voltages, and harmonic distortion with computational methods spanning wavelet, Fourier, and Forstescue transforms. Simulation results quantitatively establish that: i) GFM control architectures offer superior transient and steady-state fault performance compared to GFL architectures, ii) the performance of the virtual-impedance current limiter in GFM inverters offers better performance compared to current-reference saturation limiter, and iii) the specific choice of primary-control method has minimal impact on fault behavior of GFM inverters.

The Cascaded H-Bridge (CHB) multilevel inverter is a modular topology that uses multiple series-connected submodules (SMs) fed by individual DC sources. The commonly used level-shifted-carrier PWM scheme causes vast disparity in the share of power processed by various SMs, resulting in an unequal electrical and thermal stress, thereby reducing SM reliability. Ensuring equal power processing among all SMs is critical especially in applications such as battery and solar photovoltaics. This paper proposes two computationally efficient and easy to implement carrier-reassignment PWM techniques that result in perfect power balance under unity power factor (UPF) and zero power factor (ZPF) conditions. Mathematical analysis of real and reactive power is used to develop these modulation schemes, followed by validation using MATLAB/Simulink models. A comparison of real and reactive power balance are also provided for various PWM schemes at various power factors.

Recent surge in the adoption and grid-integration of renewable distributed energy resources (DERs) at utility scale has spurred the interest in power-electronic architectures for interface at medium-voltage (MV) grid. The constant endeavor to achieve higher power densities has brought forth the need for multi-port converter topologies capable of integrating heterogeneous energy resources through a common interface scheme. In this paper, a novel high-frequency link transformer based multi-port power converter termed Distributed-Phase-MMC (DP-MMC) is proposed for the grid-integration of DERs at MV level. The topology has several advantages such as modularity at sub-module as well as sub-system level, decoupled/independent power flow through its input ports and reduced voltage stresses in the HF-transformer windings. A simplified equivalent circuit and a phasor-based analysis are proposed for the system, which provide qualitative and quantitative insights into the power transfer mechanism across different ports. In addition, a control scheme is proposed based on this analysis for the operation of the system while injecting the required active/reactive power to the grid. The proposed scheme achieves the critical objective of unifying dispatchable storage systems with intermittent renewable energy systems at MV-level. Detailed MATLAB-Simulink results validate the overall operation and control of the proposed multi-port DP-MMC architecture.